1. Field of the Invention
The present invention relates to a current sensor which detects an electric current flowing through a current path to be measured, and more particularly relates to a current sensor which detects an electric current flowing through a current path to be measured, using a magnetoelectric conversion element.
2. Description of the Related Art
Current sensors which are attached to a current path to be measured and detect electric currents flowing through the current path to be measured, in order to control or monitor various types of electronic equipment, are well known. Hall elements and magnetoresistive elements are known current sensor of this type. Using multiple elements to improve sensitivity of magnetoelectric conversion elements, reduce effects of external magnetic fields, and so forth, is known.
There has conventionally been proposed a current sensor 900 having a recessed cutout formed to clasp a current path to be measured, which is omitted from illustration (see Japanese Unexamined Patent Application Publication No. 2001-066327), as illustrated in FIG. 17. FIG. 17 is a perspective view schematically illustrating the structure of the current sensor 900 described in Japanese Unexamined Patent Application Publication No. 2001-066327. The current sensor 900 illustrated in FIG. 17 is configured including a casing 920 in which is formed a recessed cutout 911 to receive a current path to be measured, a board 910 which is disposed inside the casing 920 and has a cutout 921, and magnetoelectric conversion elements (Hall elements here) 930 and 931 which are situated nearby the cutout 911 and output electric signals in accordance with the intensity of an magnetic field generated by an electric current flowing through a conductor. This is said to provide a current sensor 900 small in size and easy to attach.
There is also known a current sensor where four magnetic impedance elements are disposed facing each other across an electric line holding portion which holds an electric line, at the center (see EP1037056A1). This current sensor has an arc-shaped opening, serving as the electric line holding portion, formed at an engaging portion of a casing made up of a protruding portion and a recessed portion. The four magnetic impedance elements are disposed facing each other around the opening, so as to be at equal spacing in the circumferential direction.
Further, a current sensor using a greater number of magnetoelectric conversion elements in order to improve measurement precision as compared to the aforementioned conventional technology are described in Japanese Unexamined Patent Application Publication No. 2001-066327 and EP1037056A1, can be conceived. FIG. 13 is a plan view for describing a current sensor according to a comparative example. FIG. 13A illustrates a current sensor according to a comparative example 1 where eight magnetoelectric conversion elements C15 are disposed surrounding a current path CB to be measured, and FIG. 13B illustrates a current sensor according to a comparative example 2 where six magnetoelectric conversion elements C25 are disposed surrounding a current path CB to be measured. Note that all other than the current path CB to be measured, neighboring current paths CN, and magnetoelectric conversion elements C15 and C25 are omitted from illustration, to facilitate description.
As illustrated in FIG. 13, the current sensors according to the comparative examples have a great number of magnetoelectric conversion elements (C15, C25) disposed on a circumference centered on the center of the current path CB to be measured in plan view, so that the angles between neighboring magnetoelectric conversion elements (C15, C25) are at the same angle. That is to say, the magnetoelectric conversion elements C15 of the current sensor according to the comparative example 1 illustrated in FIG. 13A are situated at the vertices of a regular octagon, and the magnetoelectric conversion elements C15 of the current sensor according to the comparative example 2 illustrated in FIG. 13B are situated at the vertices of a regular hexagon. Accordingly, by summing the detection values of the magnetoelectric conversion elements (C15, C25), measurement precision can be made more difficult to deteriorate even if the position of the current path CB to be measured shifts somewhat.